JERUSALEM — An energetic and ambitious former spy who says that “guy issues” have clouded crucial Israeli government decisions is being urged to assume the country’s premiership as Prime Minister Olmert’s rule appears to be on the brink of collapse.

For Tzipi Livni, her role as vice prime minister means that in an emergency — such as the sudden illness that snatched the former prime minister, Ariel Sharon, from office last year — the position would automatically be hers.

More likely is that Mr. Olmert, 61, who is known for his dedication to jogging, will be forced out by criticism surrounding his handling of last year’s war in Lebanon, and a separate corruption scandal.

Pressure on him reached a new intensity last week with the resignation of the chief of the general staff, Lieutenant General Dan Halutz, for the Israeli army’s failures against Hezbollah in Lebanon. Since then, Mr. Olmert has faced a barrage of calls from politicians on the left and right to follow suit. One veteran left-wing member of Parliament, Yossi Beilin, demanded that the prime minister step aside specifically to make way for Ms. Livni.

Ms. Livni is a deeply private 48-year-old mother of two. One of her children is in compulsory military service, while the other is still at school. On the political stage, however, she cuts a composed and stylish figure, without resorting to power dressing. “She is not as aggressive as most of the women politicians I’ve met,” a fellow MP and former diplomat, Colette Avital, said.

Nonetheless, she is not shy of declaring her ambitions to become the country’s first female leader since Golda Meir and appears determined not to take over by default. Refusing to rule out a challenge to Mr. Olmert, she has been relentlessly burnishing her credentials and insisted recently that she was “qualified to be prime minister.”

A Livni challenge would be enormously popular with supporters of the centrist Kadima Party that Mr. Olmert still nominally leads. In a recent poll, only 8% of Kadima voters wanted him as leader — putting him in fifth place behind “none of the above,” which scored 12%. Ms. Livni topped the poll with 50%.

She is already looking and acting like a leader. While Mr. Olmert noted after the summer war in Lebanon that “a prime minister doesn’t have to have an agenda, he just has to run a country,” Ms. Livni has been actively drawing up plans for the future of Israel’s most crucial policies.

She has come up with her own ideas for establishing peace with the Palestinian Arabs, adapting the American-backed “roadmap for peace” to try to free it from stagnation.

Her frequent trips to America have helped raise her profile. As foreign minister leading Israel’s rallying cry against the nuclear ambitions of Iran, she has effectively become her country’s most prominent figure on the international stage. When the Israeli newspaper Ha’aretz reported last week that secret peace talks had been under way for two years between Israel and Syria, she was named as an instigator.

Such covert diplomacy would come naturally to Ms. Livni, who worked for Israel’s foreign intelligence service, Mossad, for four years in the 1980s, before becoming a lawyer.

She was first elected to the Knesset as a member for the right-wing Likud Party only eight years ago, but since then, with astute politicking, her rise has been assured.

Her most powerful ally was Ariel Sharon, for whom she helped broker the Jewish pullout of the Gaza Strip with his internal Likud Party critics.

When Mr. Sharon left Likud to form Kadima, Ms. Livni went with him, becoming the party’s number three. When Mr. Sharon was plunged into a coma by a stroke in January last year, she rallied behind Mr. Olmert and became number two. Now, she appears to be aiming higher still.

“There is no question that she’s ambitious for the top job,” a professor of political science who specializes in the role of women in Israeli politics, Yael Yishai, said. “She’s very capable, very talented, very shrewd, and knows what she wants.”

But Ms. Yishai predicted that Ms. Livni would face serious obstacles. “Israeli politics is very tribal, and you need military and social connections, which she doesn’t have and can’t make at her age. She’s a bit of a loner,” she said.

Ms. Livni has shown that she has had to struggle against the boys’ club atmosphere at the top levels of Israeli decision-making.

“Sometimes there are guy issues,” she said in a recent interview. Asked if there had been a “guy problem” in the conduct of the Lebanon war, she replied: “Not only in the war. In all kinds of discussions, I hear arguments between generals and admirals and such, and I say, ‘Guys, stop it.”‘

January 4, 2006: Mr. Olmert is named acting prime minister after Mr. Sharon’s incapacitating stroke. Inherits Mr. Sharon’s centrist Kadima Party. Tipped to win elections by a landslide.

March 28: Kadima wins elections by far less than expected, but Mr. Olmert insists main policy of unilateral Israeli withdrawal from West Bank will go ahead.

June 25: Corporal Gilad Shalit is captured by Palestinian Arabs and smuggled into the Gaza Strip, prompting a big Israeli army incursion. He is still in captivity.

July 12: Two Israeli soldiers seized by Hezbollah. Mr. Olmert orders a monthlong war in Lebanon, costing 150 Israeli lives. The two have still not been found, and Hezbollah is undefeated. Israel’s military reputation is damaged.

September: West Bank withdrawal is shelved in wake of war.

December 11: Mr. Olmert accidentally confirms that Israel has nuclear weapons during a German TV interview.

January 16, 2007: Criminal investigation launched against Mr. Olmert over alleged financial wrongdoing, the day before the Israeli military chief of staff resigns over Lebanon, prompting calls for the prime minister to do the same.